The seismic exploration technique explores the underground geological conditions by propagating an artificially excited seismic wave in the stratums. When a seismic wave excited at a certain place on the ground is propagated underground, reflection waves or refraction waves will be generated at stratum interfaces of different elasticity and returned to the ground surface. Special instruments may be used to record those waves and analyze the characteristics of the recorded waves (e.g., propagation time and vibration shapes of the waves), so as to accurately measure the depths and forms of those interfaces, and judge the lithology, physical properties and liquid-filled properties of the stratums.
Since the seismic record is noisy, usually the seismic reflection waves of the same point underground are excited and received at different positions, and a set of those seismic reflection wave from the same point is referred to as a seismic trace gather. By stacking seismic signals, the noise can be eliminated and the signal-to-noise ratio can be improved.
The same reflection point of seismic data collected in the field has different seismic reflection time which depends on the offset and the seismic propagation velocity, thus it is necessary to correct seismic record time of different offsets to a self-excitation and self-receiving seismic reflection time position, and this process is referred to as a Normal Move Out (NMO) correction, for the purpose of seismic signal stack.
However, the propagation velocity of the seismic wave is unknown, thus an NMO correction is usually realized by designing a series of seismic propagation velocities to perform an NMO correction processing of the seismic trace gather.
Since the volume of seismic data collected in the field is very huge, it is impossible for people to perform a velocity analysis for each seismic reflection point. Usually, a velocity analysis is performed for one seismic reflection point at an interval of several tens of traces, while a velocity of a trace gather without a velocity analysis is obtained by an interpolation of the velocity of the trace gather for which a velocity analysis has been performed. As the seismic velocities are not uniform, the interpolation velocities have certain errors more or less, and the NMO correction result cannot reach an ideal effect, thus it is difficult to correct the events of all of the seismic trace gathers into a horizontal state.